1. Field of the Invention
The present invention relates to a compact excimer laser useful for both research and industrial applications. Although the excimer laser of the present invention is compact in size, it still has high overall reliability and long operational life when compared with prior art lasers.
2. Description of the Prior Art
Prior art lasers may be of many different types but the type of laser of interest in the present application is generally referred to as an excimer or rare gas halide type laser. Various types of commercially available excimer lasers are constructed to use a wide variety of rare gas halides such as XeCl, KrCl, ArF, KrF, XeF, etc. The use of the different rare gas halides provides for the production of output energy at particular wavelengths. As an example, an excimer laser using KrF as the gas produces output energy at the wavelength of two hundred and forty eight nanometers (248 nm).
The repetition rate of an excimer laser is generally limited to a low rate. This is because, in a static gas system, the same gas volume cannot be excited repeatedly to produce output radiation pulses of high energy. The production of the high energy output pulses can only occur if the gas is allowed to return to the initial thermal state between excitations. This return can take considerable time, on the order of a second. Therefore, the pulse rate for successive high energy pulses may be limited to about one pulse per second.
In order to overcome this pulse rate limitation in an excimer laser, prior art excimer lasers use a dynamic gas system where the gas flows through the excited area. The gas volume is exchanged a number of times between excitations so as to allow a higher repetition rate for the high energy pulses. The pulse repetition rate can, therefore, be increased by flowing the gas through the discharged area at relatively high speeds.
Prior art excimer lasers are also not very reliable. One problem with prior art excimer lasers is that they generally incorporate plastic insulating material within the internal structure of the laser. Unfortunately, the plastic insulation material tends to degrade and break down in the presence of the laser gas and ultraviolet photons, thereby producing contaminants within the laser. Ultimately, these contaminants degrade the performance of the laser and the laser must be shut down for gas replenishment.
One prior art technique employed to lengthen the life of the laser before the laser must be shut down for replenishment is to utilize an external gas reprocessor to constantly provide cleaned gas to the interior of the laser. The external gas reprocessor, for example, may include a sophisticated filtering system to provide for the cleaning of dirty gas from the laser to thereby provide for the clean filtered gas to be reintroduced into the laser, and in particular to crucial areas within the laser.
Because of the various difficulties with the prior art lasers described above, the prior art excimer lasers tend to be fairly large in size. This is because of the complexities of structures located within the laser and because of the necessity for external equipment which must be provided with the laser in order to insure a relatively long operational life for the use of the laser.
Excimer lasers are increasingly located within or near clean rooms since one large use of eximer lasers is for semiconductor applications. Since the cost of providing space within a clean room is relatively high, the large, prior art, excimer lasers are often not cost effective. It is therefore desirable to provide for excimer lasers of as small a size as possible. In addition, it is desirable to produce improvements in the performance and reliability of these prior art lasers. The present invention is therefore directed to provide size, performance and reliability improvements in an excimer laser.